1. Field of the Invention
This invention relates to a reusable, carpule based dental syringe having a double-ended cannula which is to be retracted within a compact enclosure to permit the safe handling and disposal of the cannula while avoiding an accidental and possibly life-threatening needle stick.
2. Background Art
Dental syringes of the type having a pre-filled carpule of fluid medication and a double-ended hypodermic needle cannula are well known in the art for injecting such medication from the carpule to a targeted tissue area of a patient. However, at the completion of the injection, the needle cannula is typically locked in an axially extended position projecting outwardly from a distal bore formed through the syringe cylinder.
In some cases, the syringe may be used to treat a patient having a communicable disease. Prior to disposing the syringe, the needle cannula is frequently broken or destroyed to prevent reuse. Dental office workers are especially susceptible to accidental and potentially infectious needle sticks due to the careless handling or breaking of the needle and disposing of the syringe after use. The resulting mini-accident caused by an accidental needle stick typically requires a blood test for such diseases as AIDs and hepatitis. The corresponding cost and inefficiency of testing dental office workers who have received such an accidental needle stick result in considerable waste, which may be particularly damaging to a dental facility which is striving for economy.
The following U.S. patent and applications, which have been or will be assigned to the assignee of the present invention, disclose carpule based dental syringes having a retractable needle cannula and a flexible locking arm for controlling the movement of said carpule relative to the cylinder of the syringe: U.S. Pat. No. 4,767,413 issued Aug. 30, 1988; U.S. patent application Ser. No. 135,607 filed Dec. 21, 1987; and U.S. patent application Ser. No. 270,094, filed Nov. 14, 1988.